In UMTS (Universal Mobile Telecommunications System) networks, for the purpose of higher data rates, low delay and the like, Long Term Evolution (LTE) has been specified (Non-patent Literature 1). Also, for the purpose of wider bands and higher speed than LTE (may be also called LTE Rel. 8 or 9), LTE-A (may be called LTE-Advanced, or LTE Rel. 10, 11, or 12) has been specified, and a successor system (for example, also called FRA (Future Radio Access), 5G (5th generation mobile communication system), LTE Rel. 13, Rel. 14 and the like) to LTE has been studied.
In LTE Rel. 10/11, in order to realize the wider bands, Carrier Aggregation (CA) which integrates a plurality of component carriers (CCs) is introduced. Each CC is configured with the system band of LTE Rel.8 as one unit. Moreover, in CA, a plurality of CCs of the same radio base station (eNB: eNodeB) is set to a user terminal (UE: User Equipment).
Meanwhile, in LTE Rel. 12, dual connectivity (DC) is also introduced in which a plurality of cell groups (CG) of different radio base stations is set to a user terminal. Each cell group is configured by at least one cell (CC). Since a plurality of CCs of different radio base stations is integrated, the DC is also called an Inter-eNB CA or the like.
Moreover, in LTE Rel. 8-12, introduced are a frequency division duplex (FDD), which performs downlink (DL) transmission and uplink (UL) transmission in different frequency bands, and a time division duplex (TDD), which temporally switches DL transmission and UL transmission in the same frequency band.
In LTE Rel. 8-12 as described above, a transmission time interval (TTI), which is applied to the DL transmission and the UL transmission between the radio base station and the user terminal, is set to 1 ms and controlled. A TTI in the existing system (LTE Rel. 8-12) is also called a sub-frame, a sub-frame length or the like.